The invention relates to a device for punching out tissue areas from bone, with a blade whose circumferential cutting edge corresponds to the contour of a tissue area that is to be punched out.
Tissue punches of this kind, also called cartilage punches, are sold by the company Ars Arthro AG, 73728 Esslingen, Germany.
Such punches are used, for example, in autologous chondrocyte transplantation (ACT), see DGU—Mitteilungen und Nachrichten 45/2002 1, “ACT und Tissue Engineering” under the auspices of the DGU and DGOOC.
The hyaline articular cartilage of humans varies in thickness depending on topography. In the area of the patella, it can reach a layer thickness of 7 to 8 mm. Since the articular cartilage has no direct vessel or nerve attachments, it is nourished mainly through diffusion from the synovial fluid of the intraarticular space. The crosslinking of various matrix components to form the ground substance of the cartilage permits mechanical damping and almost frictionless sliding of the articular surfaces. At the cellular level, there is a complex structure of cartilage cells (chondrocytes), collagen fibres and proteoglycans. The healthy hyaline cartilage of an adult is able to tolerate loads that can amount to a multiple of the body's weight.
Damage to the articular cartilage represents a major problem in routine traumatology and orthopedics. The limited healing capacity of the hyaline cartilage has long been recognized and is mainly due to its particular structure and anatomy.
Damage to the articular surface, above all in the area of the load-bearing zone of the sliding surface of the joint, therefore entails increased risk of substantial joint damage in the sense of premature arthrosis. Known methods for biological reconstruction of full-thickness cartilage damage are in most cases suitable only for small to medium-sized defects. In cases of full-thickness cartilage damage, especially in the area of the knee joint, with a defect covering more than about 4 cm2, autologous chondrocyte transplantation (ACT) is therefore gaining increased clinical application.
In this method, a specimen of cartilage is removed arthroscopically from a non-supporting part of the joint. The cartilage cells from the biopsy specimen are isolated and are cultivated in a cell culture.
The cultivated cells are transplanted back into the cartilage defect zone during a second intervention.
The defective tissue has previously been removed from the cartilage defect zone, for which purposes a device mentioned at the outset is used for the punching operation.
In this so-called defect preparation, the edges have to be as smooth as possible and at right angles, specifically such that the prepared defect edges are delimited on all sides by stable cartilage. The defect base ought to reach as far as the subchondral bone. A cartilage punch corresponding to the size of the defect is applied and firmly pressed in. The contour of the circumferential cutting edge corresponds approximately to the contour of the tissue area to be punched out; this area can be circular, oval or of another shape. By means of a sharp spoon or a ring curette, the defective tissue area is scraped off (debrided) as far as the osteochondral zone.
The biopsy specimen produced beforehand is then transplanted back into the area that has been prepared in this way.
The known punches that are used have a continuous circumferential cutting edge that lies in one plane. The punches are usually made up of a hollow body, for example a tube, whose end edge extending approximately perpendicular to the longitudinal axis is ground down to form a cutting edge.
In practical use, it has now been found that optimal defect preparation is not possible with blades of this kind, because in most cases the bone surface from which the tissue area is to be separated is not even. As has already been mentioned, such defects occur particularly in the area of the knee joint, where the bone surface is strongly curved.
When a bone punch with a flat blade line is driven into a curved bone surface, this inevitably means that only some tissue areas can be incised to the optimal depth, while others cannot.
Remedial measures, such as tilting the punch back and forward, does not provide the desired smooth edges prepared at right angles.
It is therefore an object of the present invention to remedy this situation and to develop a device of the type mentioned in the introduction such that optimal defect preparation is possible.